In many technical fields it is required to homogenize a multi-phase flow. To this end, a mixer can be arranged in a stationary manner in a line conducting the flow, through which mixer the flow flows and in the process mixes the individual phases of the flow, which leads to the desired homogenization. Such a mixer arranged in a stationary manner subjected to a through flow is also described as static mixer. The static mixer can for example be used for the mixing of a flow having two or more fluid phases. For example, it can be that two different gases or two different liquids have to be thoroughly mixed. It is likewise conceivable to thoroughly mix at least one liquid phase with at least one gas phase, wherein at the same time the aim can be an evaporation of the liquid phase.
With modern exhaust systems a reduction of nitric oxides can be realized with the help of an SCR-catalytic converter in connection with a reduction agent fed to the exhaust gas flow. A suitable reduction agent for example is ammonia, which is preferably fed to the hot exhaust gas in liquid form in the form of a watery urea solution. In particular, the watery urea solution is injected into the exhaust gas flow. Up to the SCR-catalytic converter the injected urea solution is to be completely evaporated and homogeneously distributed in the exhaust gas flow in order to be able to realize the desired reduction of the nitric oxides. In order for this evaporation and homogenization to be realisable over as short as possible a distance, static mixers can be employed. The respective static mixer is then positioned downstream of an injection device for injecting the reduction agent and upstream of the SCR-catalytic converter.
Another possible application arises during the regeneration of particle filters, which for this purpose have to be heated to a self-igniting temperature of the deposited particles. For this purpose, an oxidation catalytic converter can be arranged upstream of the respective particle filter with which fuel can be exothermically converted, which for this purpose is injected upstream through nozzles. Because of this, the exhaust gas is greatly heated and the exhaust gas then transports the heat to the particle filter located downstream in order to heat the latter. For this application, too, mixing and evaporation of the nozzle-injected fuel with the exhaust gas is advantageous.
The use of such mixers in the exhaust system however is problematic. In order to be able to achieve an adequate homogenization even with relatively low exhaust temperatures and comparatively low flow velocities the mixer must possess a particularly high effectiveness which however is accompanied by a comparatively high through-flow resistance. At higher flow velocities, this leads to a considerable drop in power of the combustion engine. In addition it can be advantageous to arrange guide vanes of the mixer in the cross section that can be subjected to the through-flow so that in a projection of the guide vanes orientated parallel to the line longitudinal direction it is largely covered. In this manner, the risk for example of a droplet strike-through at low exhaust gas temperatures can be reduced. Such a largely “view-tight” arrangement of the guide vanes likewise results in a high through-flow resistance.
From DE 10 2008 017 395 A1 such a static mixer for the mixing of a flow in a line conducting the flow, particularly of an exhaust system of a combustion engine, is known, which comprises several guide vanes which with the known mixer are produced of usual steel plate.